The present invention relates generally to a biocidal composition that provides sustained release of a gas. The invention particularly relates to a composite for retarding, controlling, killing or preventing microbiological contamination (e.g., bacteria, fungi, viruses, mold spores, algae, and protozoa), deodorizing and/or retarding, preventing or controlling chemotaxis by release of a gas, such as chlorine dioxide, sulfur dioxide, nitrogen dioxide, nitric oxide, nitrous oxide, carbon dioxide, hydrogen sulfide, hydrocyanic acid, dichlorine monoxide, or chlorine.
Chlorine dioxide (ClO.sub.2) is a superior oxidizing agent widely used as a bleach, disinfectant, fumigant or deodorizer. It can penetrate the cell wall or membrane and cytoplasm of mold spores, bacteria and other microbiological contaminants at concentrations below one part per million and destroy them.
The incorporation of chlorine dioxide or sodium chlorite in food packaging has prompted studies to determine whether residual levels of such preservatives result in a significant genetic or carcinogenic hazard to humans. Meier et al. studied the effect of subchronic and acute oral administration of chlorine, chlorine dioxide, sodium chlorite and sodium chlorate on the induction of chromosomal aberrations and spermhead abnormalities in mice [Environ. Mutagenesis, 7, 201 (1985)]. Only the highly reactive hypochlorite resulted in a weak positive effect for mutagenic potential. The other compounds, including chlorine dioxide and sodium chlorite, failed to induce any chromosomal aberrations or increased numbers of micronuclei in the bone marrow of mice. Vilagines et al. attribute the relatively innocuous effect of chlorine dioxide to its inability to produce halomethanes, unlike hypochlorite and chlorine [Proc. AWWA Disinfect. Semin., 24 pp. (1977); Chem. Abs. 93, 173513f]. Recently, Richardson et al. reported that an extensive study of the reaction of chlorine dioxide with water borne organics by the Environmental Protection Agency confirmed this observation [Environ. Sci. Technol., 28, 592 (1994)].
Japanese Kokai Nos. 63/296,758, 63/274,434, and 57/168,977 describe deodorants containing chlorine dioxide incorporated in a polymer, ceramic beads, or calcium silicate wrapped in nonwoven cloth, respectively. Gels that generate chlorine dioxide for use as topical applications for disinfection are disclosed by Kenyon et al., Am. J. Vet. Res., 45(5), 1101 (1986). Chlorine dioxide generating gels are generally formed by mixing a gel containing suspended sodium chlorite with a gel containing lactic acid immediately prior to use to avoid premature chlorine dioxide release. Chlorine dioxide releasing gels have also been used in food preservation.
Encapsulation processes have also been used in preparing sources of chlorine dioxide. Canadian Patent No. 959,238 describes generation of chlorine dioxide by separately encapsulating sodium chlorite and lactic acid in polyvinyl alcohol and mixing the capsules with water to produce chlorine dioxide.
Tice et al., U.S. Pat. No. 4,585,482 describe gradual hydrolysis of alternating poly(vinyl methyl ether-maleic anhydride) or poly(lactic-glycolic acid) to generate acid that can release chlorine dioxide from sodium chlorite. A polyalcohol humectant and water are encapsulated with the polyanhydride or polyacid in a nylon coating. After sodium chlorite is diffused into the capsule through the nylon wall, an impermeable polystyrene layer is coacervated around the nylon capsule. Solvents are required for reaction and application of the capsules. The capsules can be coated onto surfaces to release chlorine dioxide. Although the capsules are said to provide biocidal action for several days to months, chlorine dioxide release begins immediately after the capsules are prepared. The batchwise process used to prepare the capsules also involves numerous chemical reactions and physical processes, some of which involve environmental disposal problems.
Powders that release chlorine dioxide as soon as they are prepared have been formed by mixing acid solids and chlorite solids. Lovely, U.S. Pat. No. 3,591,515 describes a chlorite-containing powder that releases chlorine dioxide upon being admixed with an acid-containing powder. Hartshorn, U.S. Pat. No. 4,104,190 describes solid mixtures of sodium chlorite and citric, adipic or malic acid that are compressed to form tablets. Mason et al., U.S. Pat. Nos. 4,547,381 and 4,689,169 disclose mixtures of powdered sodium chlorite, acid and inert diluent that release chlorine dioxide without exposing the mixtures to ambient moisture. Tice et al., U.S. Pat. No. 4,585,482 describe solid admixtures of sodium chlorite and polylactic acid.
Wellinghoff et al. have formulated composites that include a hydrophobic phase containing an acid releasing agent and a hydrophilic phase containing chlorite anions. The composite is substantially free of water and gas (e.g., chlorine dioxide) until it is exposed to moisture. Once exposed to moisture, acid and hydronium ions are generated in the hydrophobic phase. The hydronium ions migrate to the hydrophilic phase and react with chlorite anions to generate chlorine dioxide from the composite. These composites are composed of and generate only substances used in foods or substances generally recognized as safe or inert substances. The composites can be used for food packaging and other applications where the substances can be ingested by or in contact with humans. These composites are described in U.S. Pat. Nos. 5,360,609, 5,631,300, 5,650,446, 5,668,185, 5,705,092 and 5,707,739.
Wellinghoff et al. U.S. patent application Ser. No. 08/924,684 discloses a composite formulated for maximum chlorine dioxide release in which the hydrophilic material contains an .alpha.-amino ether, ester or alcohol and a chlorite salt formed by reaction of an iminium chlorite and a base. Iminium chlorite is unstable to nucleophilic attack by the chlorite anion. When the iminium chlorite is reacted with a base, however, the more stable a-amino ether, ester or alcohol and a chlorite salt are formed.
Wellinghoff et al. U.S. Pat. No. 5,639,295 describes a method for maximizing chlorine dioxide release from an amine-containing composite by omitting the chlorite source until the composite is applied to a surface. After application, the composite is exposed to chlorine dioxide gas that either reacts with the amine to form iminium chlorite in situ or reacts with the amine to provide chlorite anions. The composite is then activated in the presence of moisture to release chlorine dioxide. The composite can be exposed to elevated temperatures during processing, storage and application because the hydrophilic material does not contain iminium chlorite or any chlorite anions that could decompose at such temperatures. The method also precludes premature release of chlorine dioxide from the composite.
Barenberg et al. U.S. patent application Ser. No. 08/723,907 describes numerous methods of using composites such as those disclosed by Wellinghoff et al. to retard bacterial, fungal, and viral contamination and growth of molds on food, produce, meat, and other materials and to deodorize materials such as textiles and storage spaces.
Wellinghoff et al. U.S. patent application Ser. No. 08/651,876 describes transparent compositions that provide sustained release of chlorine dioxide.
There is a need for an inert composition that can be easily activated to initiate chlorine dioxide release in use. A composition that is composed of and generates only substances used in foods, or those generally recognized as safe or inert substances, is particularly needed for food packaging and other applications where the substances can be ingested by or in contact with humans.